The present invention relates to a photocurable resin composition useful for forming a fine pattern, and a method for forming a pattern using such a resin composition.
In recent years, there have been seen rapid advancement in miniaturization and integration of semiconductor integrated circuits, and efforts have been made for higher precision of photolithography applied as a pattern transfer technique for realizing finer working of such circuits. However, the conventional working process has approached the wavelength of the light source used for light exposure, and the lithographical techniques have come close to the limitation. In order to push forward with further advancement of miniaturization and higher precision, an electron beam direct writing system, which is a kind of charged corpuscular beam devices, has come to be used superseding the conventional lithographical techniques.
Pattern forming using the electron beams, unlike the blanket exposure method in pattern forming using a light source such as i-beam or excimer laser, is a method in which the mask patterns are drawn. Therefore, the greater the number of patterns to be drawn, the more time is required for exposure (drawing), hence a longer time for pattern forming, and this has been a drawback to this method. Accordingly, as the degree of integration is elevated drastically, with the memory capacity increasing to, say, 256 megabytes and further up to 1 and then to 4 gigabytes, the patterns are also made dense correspondingly to so much elongate the time for pattern forming, and it is feared that this may lead to excess deterioration of throughput. In view of this, in order to realize higher speed operation of the electron beam direct writing devices, efforts have been made for the direct writing of a blanket pattern irradiation method in which the masks of various configurations are used in combination, and electron beams are applied to them en bloc to form electron beams of intricate configurations. As a consequence, while higher pattern densification has been advanced, enlargement in size and structural complication of the electron beam direct writing devices have become essential, resulting in a disadvantage of high production cost.
Techniques for forming the fine patterns at low cost are disclosed in Patent Documents 1 and 2 listed below. In these techniques, a mold having raggedness of the same pattern as that formed on the substrate is impressed to a resin layer formed on the surface of a transfer substrate to thereby transfer the specified pattern. Particularly, according to the nanoimprinting techniques disclosed in Patent Document 2 and Non-Patent Document 1, transfer of fine structures of less than 25 nanometers in size is made possible by using a silicon wafer as the mold.
[Patent Document 1] U.S. Pat. No. 5,259,926
[Patent Document 2] U.S. Pat. No. 5,772,905
[Patent Document 3] JP-A H5-98112
[Patent Document 4] JP-A H5-100423
[Patent Document 5] JP-A 2002-156763
[Patent Document 6] JP-A H10-153864
[Non-Patent Document 1] S. Y. Chou et al:
Appl. Phys. Lett., Vol. 67, p. 3114 (1995)
[Non-Patent Document 2] Yuichi Kurashima:
Jpn. J. Appln. Phys., Vol. 42, p. 3871
The nanoimprinting techniques can be roughly divided into two types depending on the material to be transferred. One type is a thermal nanoimprinting technique according to which the material to be transferred is heated to make plastic deformation by the mold, and then the material is cooled to form a pattern. Another type comprises an optical nanoimprinting technique in which after a substrate has been coated with a photocurable resin which is liquid at room temperature, a light-transmittable mold is pressed against the resin and light is applied to cause curing of the resin on the substrate to form a pattern. Especially, the optical nanoimprinting technique, as it enables pattern forming at room temperature, has the advantage in that there scarcely takes place strain due to difference in linear expansion coefficient between the substrate and the mold on heating, allowing high-precision pattern forming, so that attention is focused on this technique as a substitute for conventional semiconductor lithography. Regarding the photocurable resins usable in such optical nanoprinting systems, PAK-01 (product by Toyo Gosei KK) is introduced in Non-Patent Document 2.
Also, with reference to the photocurable resins, Patent Documents 3 and 4 disclose the etching resist compositions incorporated with photopolymerization initiators using acrylate monomers as starting material. Patent Documents 5 and 6 disclose etching resist compositions with excellent etching resistance.